Any light source can be uniquely characterized by its spectrum plot, that is, the amount of light at each wavelength. Correlated color temperature (CCT) is used to characterize the light in the measurement of black body radiator's color hue. Therefore CCT is suited for characterizing a light source that is indeed close to black body radiator in terms of light spectrum, i.e., those on a line from reddish-orange to yellow and more or less white to bluish white. CCT is not suited for measuring the color temperature of a green or purple light, for example, because their hue and spectrum is far from black body radiator. Color temperature can be a useful description of light for photographic applications, as light sources such as daylight and tungsten bulbs closely mimic the distribution of light created by blackbodies, although others such as fluorescent and most commercial lighting depart from blackbodies significantly.
A digital camera is typically equipped with a camera flash unit or sub-unit calibrated to a single color that approximates sunlight. In conditions of low ambient light or scene illumination, the camera flash unit emits a flash of artificially generated light during image capture. Together with the available ambient light, the flash light emitted from the camera flash unit increases overall scene illumination to allow for brighter images. In photography, the type of ambient lighting can dictate the CCT of the image scene (i.e., daylight, fluorescent light, tungsten, etc.). When flash is used, the output color of the flash may not match the CCT of the image scene, resulting in images generated under different ambient light conditions exhibiting particular color casts. When the color temperature of ambient light and the emitted flash color do not match, unnatural-looking white balance such as varying color casts in foreground and background objects can occur in captured images.
In some cases, a dual color light-emitting diode (LED) flash can be matched to a determined CCT of ambient light in order to enable the camera's white balance algorithm to perform better. However, use of two LEDs only allows a linear range of possible colors of the output lighting, better matching some ambient lighting but excluding others. As such, color casts in captured images can be reduced but may not eliminated, in all cases, because the ability to match output lighting color to ambient light color temperature is limited. In some examples, if the output color of the flash does not match the color temperature of the ambient lighting, this can result in a captured image with different color casts from the flash and the ambient light, complicating performing white balance on the captured image. In addition, it can be difficult to select the two LEDs to match the sensor due to manufacturing variations for both the LED output colors and the sensor response. Further, use of determined CCT of ambient light to determine the combined output color of the LEDs may not provide the most suitable flash output color for the camera's white balance process.